HTTP Status Code Reference

An HTTP status code is a three-digit number a server returns with every response, telling the browser, crawler, or API client what happened to the request. This reference groups the codes into their five classes and explains the ones you will actually encounter, along with how each affects users and search engines.

How to use it

1. Find the status code you received in your browser console, server logs, or an API response.
2. Match the first digit to its class below to understand the general category (success, redirect, client error, or server error).
3. Look up the specific code to read its precise meaning and the typical cause.
4. Check whether it is permanent or temporary, since that decides whether to fix configuration, retry the request, or update a link.

The five status code classes

Every code falls into one of five ranges, signalled by its leading digit:

Class	Meaning
1xx	Informational — request received, processing continues
2xx	Success — the request was understood and accepted
3xx	Redirection — further action is needed to complete the request
4xx	Client error — the request was malformed or not allowed
5xx	Server error — the server failed to fulfil a valid request

The codes that matter most in day-to-day work: 200 OK, the standard success response. 301 is a permanent redirect that passes ranking signals to the new URL, while 302 is temporary and keeps the original URL indexed. 304 Not Modified tells the browser its cached copy is still valid. 400 means a bad request, 401 requires authentication, and 403 means access is forbidden even when authenticated. 404 Not Found signals a missing resource, whereas 410 Gone confirms it was removed deliberately and permanently. 429 Too Many Requests indicates rate limiting. On the server side, 500 is a generic internal error, 502 a bad gateway, and 503 a service that is temporarily unavailable.

FAQ

What is the difference between 301 and 302 for SEO?

A 301 permanently moves a page and tells search engines to transfer ranking signals to the destination and index it instead. A 302 is temporary, so engines keep the original URL indexed. Using 302 when you meant 301 can prevent the new URL from ever taking over in results.

Should I use 404 or 410 for deleted pages?

Both keep a page out of search results. A 404 suggests the resource might return, so crawlers may revisit it. A 410 states the page is permanently gone, which can prompt faster removal from the index. Use 410 when you are certain the content will never come back.

What does a 429 mean and how do I respond?

A 429 means you have sent too many requests in a given window and have been rate limited. Responses often include a Retry-After header indicating how long to wait. Slow your request rate or back off exponentially before trying again.

Are 5xx errors my fault or the server's?

5xx codes signal a server-side failure, not a problem with your request. A 502 or 503 usually points to an overloaded or misconfigured backend or gateway. They are often temporary, so retrying after a short delay is reasonable, but persistent 5xx errors need investigation on the server.